Quantitative studies are being made on covalent addition of nucleophilic reagents such as water, bisulfite ion, phenoxides, amines, etc., to heterocyclics. The latter include uracils, 5-azacytidine, acridines, tryptamine and others. Various factors which influence the rate and extent of these reactions are under study. Among the goals of these studies are (1) possible stabilization of unstable species such as 5-azacytidine through prodrug modification, (2) understanding certain biochemical reactions mediated by such addition reactions, and (3) development of new anticancer drugs which would contain both intercalating and alkylating capability.